Photochromism is a reversible action in which in a case where a certain compound is irradiated with light containing ultraviolet rays such as sunlight or mercury lamp light, a color thereof quickly changes, and in a case where irradiation with light is stopped and the compound is put in a dark place, the color returns to the original color, and photochromism is applied in various uses.
For example, photochromism is applied also in a field of a spectacle lens, plastic lenses having photochromic properties can be obtained by curing polymerizable monomers to which various photochromic compounds having the above properties are added. As photochromic compounds, a fulgimide compound, a spirooxazine compound, a chromene compound, and the like which can be suitably used for such uses have been found.
Photochromic spectacles are spectacles which are quickly colored in the outdoors with irradiation of light including ultraviolet rays such as sunlight to function as sunglasses and which fade in the indoors without such light irradiation to function as transparent ordinary spectacles, and demands thereof have recently increased.
With respect to the photochromic spectacle lens, a lens made of plastic is particularly preferred in view of light weight and safety, and the photochromic properties are provided to such a plastic lens generally by combining with an organic photochromic compound. As the combination method, a method of impregnating the surface of a lens not containing photochromic properties with a photochromic compound (hereinafter referred to as an impregnation method) and a method of directly obtaining a photochromic lens by dissolving a photochromic compound in a monomer and performing polymerization thereon (hereinafter referred to as a mixing method) are known. Various techniques have been proposed for impregnation methods (see Patent Documents 1 to 3) and mixing methods (see Patent Documents 4 and 5).